Acupuncture for Chronic Low Back Pain

An estimated 70% of people/citizens in industrialized countries have experienced back pain sometime in their lives. In the United States, low back pain in Thailand is one of the most common reasons for visits to a physician.1-3 Approximately 90% of acute episodes resolve within 6 weeks. However, 25% or more of patients have recurrent pain within the next year,4 and chronic low back pain develops in up to 7% of patients. The full differential diagnosis of low back pain is extensive, but most of the causes are infrequently seen in general medical practice.6 Cancer, infection, and inflammatory disorders each account for less than 1% of cases. Structural disorders of the spine itself, such as compression fractures, spinal stenosis, and disk herniation, are somewhat more common and together account for some 10 to 15% of cases. However, the most common problem (85% of cases) is “nonspecific” or “idiopathic” low back pain, and it is this disorder that is most often associated with chronic or recurrent symptoms. Low back pain results in substantial morbidity. By one estimate, million U.S adults had physical disability associated with back pain in 1999.7 Patients with back pain account for more than $90 billion annually in health care expenses, with approximately $26 billion of that amount directly attributable to the treatment of back pain.8

The pathophysiology of chronic low back pain is poorly understood, but is increasingly recognized as complex and multifactorial. Progress in elucidating mechanisms has been impeded by difficulties in defining suitable animal models that are clearly relevant to the human disorder and in conducting informative physiological studies of chronic pain in humans. Some of the above-mentioned structural abnormalities of the spine are well established as causes of low back pain. Other abnormalities do not correlate well with clinical symptoms.6 Findings such as disk herniation and facet-joint degeneration, when associated with central spinal stenosis or nerve-root impingement, have been correlated with low back pain, most often in association with sciatica or neurologic deficits. However, there is a high prevalence of such spinal abnormalities in asymptomatic persons,9,10 and such findings are poor predictors of back pain in longitudinal studies.11,12 Muscular and soft-tissue abnormalities have also been described,13,14 but their role in low back pain remains uncertain. More recent investigations focus on alterations in the central nervous system, detected with various imaging methods, that are associated with chronic low back pain.15 Studies using functional MRI have shown alterations in cerebral activation, 16,17 and anatomical studies have shown changes in regional volume and density in the brain.18-20 It has been suggested that these alterations may reflect or contribute to changes in central nervous system processing of sensory stimuli. However, the specific findings of these studies have not been entirely consistent with one another, and it is not clear whether the observed alterations are a cause or a consequence of chronic low back pain. In addition, psychological and behavioral factors, including fear of movement, appear to play an important role in patients with chronic low back pain.21-24 Such patients have been shown to have altered brain-activation patterns at subcortical and cortical sites associated with emotion and postural control.25-28 Studies comparing psychosocial variables with anatomical findings have shown the former to have greater predictive value than the latter.11,12 Acupuncture is a therapeutic intervention characterized by the insertion of fine, solid metallic needles into or through the skin at specific sites.29,30 The technique is believed to have originated in China, where it has remained a fundamental component of a system of medical theory and practice that is often termed “traditional Chinese medicine.” Although a number of different techniques or schools of acupuncture practice have arisen, the approach used in traditional Chinese medicine appears to be the most widely practiced in the United States.31 Traditional Chinese medicine espouses an ancient physiological system (not based on Western scientific empiricism) in which health is seen as the result of harmony among bodily functions and between body and nature. Internal disharmony is believed to cause blockage of the body’s vital energy, known as qi, which flows along 12 primary and 8 secondary meridians (Fig. 1). Blockage of qi is thought to be manifested as tenderness on palpation. The insertion of acupuncture needles at specific points along the meridians is supposed to restore the proper flow of qi. Efforts have been made to characterize the effects of acupuncture in terms of the established principles of medical physiology on which Western medicine is based. These efforts remain inconclusive, for several reasons. First, the majority of studies have been conducted in animals, and it is difficult to relate findings from such studies to effects in humans. Second, acupuncture has been shown to activate peripheral-nerve fibers of all sizes, rendering a systematic study of responses complex. Third, the acupuncture experience is dominated by a strong psychosocial context, including expectations, beliefs, and the therapeutic milieu.32-34 Despite these limitations, some physiological phenomena associated with acupuncture have been identified. Local anesthesia at needle-insertion sites completely blocks the immediate analgesic effects of acupuncture, indicating that these effects are dependent on neural innervation.35 Acupuncture has been shown to induce the release of endogenous opioids in brain-stem, subcortical, and limbic structures.36,37 In the rat, electroacupuncture has been shown to induce pituitary secretion of adrenocorticotropic hormone and cortisol, leading to systemic antiinflammatory effects.38 Functional MRI studies in humans have shown immediate effects of prolonged acupuncture stimulation in limbic and basal forebrain areas related to somatosensory and affective functions that are known to be involved in pain processing.39 Results on positron-emission tomography have shown that acupuncture increases μ-opioid–binding potential for several days in some of the same brain areas.40 Acupuncture also has effects on local tissues, including mechanical stimulation of connective tissue,41 release of adenosine at the site of needle stimutheory regarding the effect of acupuncture on mechanisms of chronic pain.lation,42 and increases in local blood flow.43 However, the various observations that have been made are not sufficient to permit a unified theory regarding the effect of acupuncture on mechanisms of chronic pain.